A drum brake can in principle be embodied differently according to different construction principles (simplex, duplex, duo-duplex, servo, duo-servo). A uniform constructional advantage of drum brakes is their self-energizing effect in at least one direction of rotation, so that in principle it is possible to forego a brake power assist unit.
In order to achieve a parking brake function in an electromechanical manner, a central electromechanical actuator is conventionally provided in addition to the conventional hydraulic wheel brake actuating members of a service brake system, which central electromechanical actuator comprises an electric motor and a reduction gearing and also a threaded nut-spindle arrangement that influences at least one brake shoe of a drum brake by way of a comparatively long actuating pull. As a consequence, an electromechanical parking brake (EPB) is produced that is universally suitable not only for small vehicles and light vehicles but also for heavy vehicles.
Parking brakes than can achieve the parking brake function are known, said parking brakes are furthermore electromechanically actuable parking brakes having an expansion lock that is arranged in a guide in such a manner as to be axially displaceable (floating). The expansion lock comprises two actuating elements that can be displaced in a translatory manner and influence the brake shoes in a counter direction. In each case, a gear train having reduction gearing is integrated into the actuator so that the expansion lock acts directly on the brake shoes.
There is a need to improve the costs of constructing known electromechanically actuable drum brake parking systems and to reduce the installation space required by said systems. The parking brake cable pull systems having a central actuator are disadvantageous because it is necessary for the vehicle manufacturer to separately install and link the cable pull to the wheel brake, so that the process of finally assembling the actuator, actuating pull and wheel brake can only be performed at the assembly belt of the vehicle manufacturer which increases the complexity of production in this region. Vehicle manufacturers always desire a particularly cost-effective, modular vehicle production that is as uncomplicated as possible. In addition, the scope of function of a parking brake is to be extended to a potential service brake function.
For this reason, EP 0 920 390 B1, which is incorporated by reference, discloses an electromechanically actuable drum brake module having a particularly small overall installation size. An outer periphery of a cylindrical actuating unit is inserted through an orifice in an anchor plate. A rotatable drive nut is supported by way of the motor housing on a support plate. In order to shorten the structural length of the actuating unit it is provided that a rotor of a particularly embodied electric motor radially encompasses the outer side of a spindle arrangement and guides said spindle arrangement in a rotatably fixed manner. This type of construction requires an electric motor that is dimensioned in order to provide a comparatively high level of energy and comprises a special housing together with an especially adapted support plate.
An electromechanically actuable duo-servo drum brake without a cable pull linkage is known from EP 594 233 B1, which is incorporated by reference. An electric motor is arranged on a rear face of an anchor plate. The motor axis is arranged at a right angle with respect to the axis of rotation of a brake drum and drives a threaded spindle that is positioned in a rotatable and also axially non-displaceable manner. The threaded spindle is provided in parallel to the motor axis in the brake drum and is mounted in a housing. The threaded spindle engages an element that is mounted in an axially displaceable and non-rotatable manner in the housing, which element influences a lever gear. In addition to an electric motor that is dimensioned in order to provide a comparatively high level of energy, this type of construction still requires further components that are embodied in an extremely special manner and therefore do not allow any simple variation in the production series. Problems arise if the engine is switched off when the brakes are hot.